Researchers probe the next generation of 2-D materials

As the properties and applications of graphene continue to be explored in laboratories all over the world, a growing number of researchers are looking beyond the one-atom-thick layer of carbon for alternative materials that exhibit similarly captivating properties.

One of these materials is molybdenum disulfide (MoS2), which is part of a wider group of materials known as transition metal dichalcogenides, and has been put forward by a group of researchers in the US as a potential building block for the next generation of low-cost electrical devices.

Due to its impressive ability to convert light into electricity at an extremely efficient rate, single layers of the semiconducting material have been used to fabricate a widely used device known as a photosensor, which is found in a range of appliances from solar panels and digital cameras to remote controls.

The device has been presented today, 4 April, in the very first issue of IOP Publishing's new journal 2D Materials--a multidisciplinary journal with a focus on applications and fundamental science concerning all aspects of graphene and 2D materials.

In their study, the researchers highlighted the suitability of MoS2 by successfully demonstrating the photosensor's ability to efficiently convert the energy from photons, delivered to the device in two separate wavelengths by a laser, into an electric current.

Lead author of the research, Nestor Perea-Lopez, from The Pennsylvania State University, said: "The thinnest foil of MoS2 has a thickness of three atoms. One can picture this monolayer foil as a sandwich, where sulfur atoms are the bread and molybdenum is the ham. The monolayer is even more interesting than the material in bulk, because in such thin form it can convert photons into electrons very efficiently, making it an ideal material to use in light detectors, such as the ones used in digital cameras."

A significant challenge that remains for researchers working with 2D materials is how to produce the materials in bulk. Graphene, for example, can only be produced in bulk through a liquid phase or by exfoliating graphite into very thin layers or flakes, which can be very difficult to control.

The goal is to be able to synthesize 2D materials using a bottom-up approach, carefully piecing individual components together like building blocks.

The researchers did this successfully in their study by growing tiny triangles of single-layered MoS2, around five micrometers wide, onto a silica-based substrate using a bottom-up process known as chemical vapour deposition.

"The devices we built are very small which means that we could integrate millions in a few millimeter squares," said Perea-Lopez.

On the suitability of MoS2 as an alternative to graphene, Perea-Lopez continued: "Graphene is a semi-metal, which means that electrons can move through the material very fast even with very small voltages; however, this is both an advantage and disadvantage, since electronic devices need to have an 'on' and 'off' state. Graphene devices can therefore be hard to turn off, but MoS2 has a large energy gap that allows it to have very large on/off ratios of hundreds of millions.

"Not everything about graphene is wrong though, and the path in this field must be the integration of metals and semi-metals, such as graphene, with insulators such as boron nitride and semiconductors like MoS2 to create the next generation of devices."

1. For further information, a full draft of the journal paper or contact with one of the researchers, contact IOP Press Officer, Michael Bishop: Tel: 0117 930 1032 E-mail: michael.bishop@iop.org For more information on how to use the embargoed material above, please refer to our embargo policy.

IOP Publishing Journalist Area

2. The IOP Publishing Journalist Area gives journalists access to embargoed press releases, advanced copies of papers, supplementary images and videos. In addition to this, a weekly news digest is uploaded into the Journalist Area every Friday, highlighting a selection of newsworthy papers set to be published in the following week. Login details also give free access to IOPscience, IOP Publishing's journal platform. To apply for a free subscription to this service, please email Michael Bishop, IOP Press Officer, michael.bishop@iop.org, with your name, organisation, address and a preferred username.

3. The published version of the paper 'CVD-grown monolayered MoS2 as effective photo sensor operating at low-voltage' (N Perea-López et al 2014 2D Materials 1 011004) will be freely available online from 4 April. It will be available at http://iopscience.iop.org/2053-1583/1/1/011004/article

2D Materials

4. 2D Materials is a multidisciplinary, electronic-only journal devoted to publishing fundamental and applied research of the highest quality and impact covering all aspects of graphene and related two-dimensional materials.

IOP Publishing

5. IOP Publishing provides a range of journals, magazines, websites and services that enable researchers and research organisations to reach the widest possible audience for their research. We combine the culture of a learned society with global reach and highly efficient and effective publishing systems and processes. With offices in the UK, US, Germany, China and Japan, and staff in many other locations including Mexico and Russia, we serve researchers in the physical and related sciences in all parts of the world. IOP Publishing is a wholly owned subsidiary of the Institute of Physics. The Institute is a leading scientific society promoting physics and bringing physicists together for the benefit of all. Any profits generated by IOP Publishing are used by the Institute to support science and scientists in both the developed and developing world. Go to ioppublishing.org.

Access to Research

6. Access to Research is an initiative through which the UK public can gain free, walk-in access to a wide range of academic articles and research at their local library. This article is freely available through this initiative. For more information, go to http://www.accesstoresearch.org.uk

The Institute of Physics

6. The Institute of Physics is a leading scientific society. We are a charitable organisation with a worldwide membership of more than 50,000, working together to advance physics education, research and application. We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications. Go to http://www.iop.org.

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.